The space telescope was being designed to locate 90% of the asteroids greater than 140 metres (460 ft) in diameter that exist in near-Earth orbits. The telescope would have orbited the Sun in a Venus-like orbit (i.e. between Earth and the Sun), and was being designed to catalog 90% of the large asteroids in Earth’s region of the Solar System. The craft would have been placed in an orbit similar to that of Venus, allowing it to clearly view the night half of the sky every 20 days, and picking out objects that are currently often difficult, if not impossible, to see in advance from Earth."[5] Sentinel would have had an operational mission life of from six and a half to ten years.[6]

After NASA terminated their funding agreement with the B612 Foundation in October 2015[7] and the private fundraising goals could not be met, the Foundation eventually opted for an alternative approach using a constellation of much smaller spacecraft under study as of June 2017[update].[1] NASA/JPL's NEOCam has been proposed instead.

As of April 2013[update], B612 was attempting to raise approximately $450 million in total to fund the total development and launch cost of Sentinel, at a rate of some $30 to $40 million per year.[5] That funding profile excludes the advertised 2018 launch date.

After NASA terminated their $30 million funding agreement with the B612 Foundation in October 2015[7] and the private fundraising did not achieve its goals, the Foundation eventually opted for an alternative approach using a constellation of much smaller spacecraft which is under study as of June 2017[update].[1] NASA/JPL's NEOCam has been proposed instead.

Unlike similar projects to search for near-Earth asteroids or near-Earth objects (NEOs) such as NASA's Near-Earth Object Program, Sentinel would have orbited between Earth and the Sun. Since the Sun would therefore always have been behind the lens of the telescope, it would have never inhibited the telescope's ability to detect NEOs and Sentinel would have been able to perform continuous observation and analysis.

The telescope was intended to measure 7.7 metres (25 ft) by 3.2 metres (10 ft) mass 1,500 kilograms (3,300 lb) and would have orbited the Sun at a distance of 0.6 to 0.8 astronomical units (90,000,000 to 120,000,000 km; 56,000,000 to 74,000,000 mi) approximately in the same orbital distance as Venus. It would have employed infrared astronomy methods to identify asteroids against the cold of outer space. The B612 Foundation worked in partnership with Ball Aerospace to construct Sentinel's 0.51 m (20 inches) aluminum mirror, which would have captured the large field of view.[4]
"Sentinel will scan in the 7- to 15-micron wavelength using a 0.5-meter infrared telescope across a 5.5 by 2-deg. field of view. The [infrared] IR array would have consisted of 16 detectors, and coverage would have scanned a 200-degree, full-angle field of regard."[5]

REP. STEWART: ... are we technologically capable of launching something that could intercept [an asteroid]? ... DR. A'HEARN: No. If we had spacecraft plans on the books already, that would take a year ... I mean a typical small mission ... takes four years from approval to start to launch ...